Passenger automotive vehicles are commonly equipped with air bag restraint devices for mitigating potential injuries to vehicle occupants for certain types of vehicle accidents. For example, front impact air bags are frequently installed in the steering column and dash in the front of passenger vehicles, while side impact air bags are side mounted on the roof rail. Automotive air bag systems typically include an initiator, such as an ignitor, for actuating a pyrotechnic charge which generates gas, such as nitrogen, to inflate the air bag. Vehicle crash sensors, such as accelerometers, are typically used to detect the onset of an accident. The sensed signals are processed to predict the occurrence of certain crash events which are severe enough to warrant the activation of the air bag. The air bag is electronically deployed to provide a restraining force for the vehicle occupant.
The air bag restraining force should be sufficient to counteract the kinetic energy of the occupant to slow the occupant down so that the occupant's velocity is substantially matched to that of the vehicle before the occupant impacts the vehicle interior. Air bag restraint systems can be designed to operate over a wide range of vehicle conditions. These conditions may include a range of speeds, passenger sizes, seating positions, and the presence of belted or unbelted occupants, all of which may affect the air bag design requirements. Higher velocity speeds and larger passengers result in a larger kinetic energy and, thus, generally require greater opposing restraining forces. Smaller occupants and occupants seated close to the steering wheel generally require lower restraining forces.
To accommodate the above-described conditions, the amount of restraining force generated by the air bag may need to be varied in order to optimize the air bag performance. The amount of restraining force that the air bag applies is a function of both the mass of gas filling the air bag and the size of any vent holes. Additionally, the ambient temperature of the inflator module affects the temperature of the gas filling the air bag. The gas is significantly cooled as it passes through the various screens and the output ports of the inflator. Lower ambient temperatures can reduce the resultant gas pressure which creates a corresponding reduction in the generated restraining force. As a consequence, the amount of restraining force generated by a conventional air bag may vary as a function of the ambient temperature of the inflator.
It is therefore desirable to provide for an air bag system in a vehicle which compensates for ambient temperature variations associated with the air bag. In addition, it is desirable to provide for an air bag control system which compensates for the ambient temperature conditions so as to optimize performance of the air bag over a wide temperature range.